1. Technical Field
The present application relates to a 3D image shooting apparatus and endoscope that can obtain surface microfacet information and a high definition image that surpass information to be normally obtained by an image sensor from a two-dimensional light intensity image.
2. Related Art
An endoscope captures an image of an organism's organ by irradiating the entire wall surface of the organ, which is covered with a mucosa, with illuminating light. In the field of such endoscopes, in order to observe microfacets on the wall surface of the organ, it is important to extract information about the depth of the object. Meanwhile, in the field of surgical endoscopes, the region in surgery should be monitored three-dimensionally. To meet these demands, technologies for three-dimensional (3D) endoscopes have been developed. A 3D endoscope ordinarily adopts a “stereo vision system” that uses two lens-image sensor sets to obtain multi-viewpoint images by viewing the object from multiple different points. Such a stereo vision system can obtain a pair of multi-viewpoint images with parallax (which may be a left-eye image and a right-eye image, for example) from the same object at the same time, and therefore, can get information about the 3D shape of the object based on the multi-viewpoint images. However, it is difficult for a stereo vision system to perfectly match the characteristics of its two image sensors to each other, which is a problem with such a system. Thus, to avoid such a problem, a technology for a “single vision system” that uses only one lens-image sensor set to obtain multi-viewpoint images as disclosed in Patent Document No. 1 has attracted a lot of attention these days.
FIGS. 16(a) and 16(b) illustrate a configuration for a conventional 3D endoscope. Specifically, FIG. 16(a) schematically illustrates an overall configuration for the 3D endoscope and FIG. 16(b) is a schematic cross-sectional view illustrating a portion of the endoscope as viewed from over it.
As shown in FIG. 16(a), this conventional endoscope includes not only an ordinary color image capturing system that uses a lens 1307 and a CCD 1308 but also an image capturing system that is specially designed to obtain multi-viewpoint images (which will be referred to herein as a “parallax image capturing system”). In the parallax image capturing system, a light transmitting section 1302 is arranged between an optical imaging section 1301 and an image capturing section 1303. As shown in FIG. 16(b), the light transmitting section 1302 has two openings 1304a and 1304b, which are arranged side by side horizontally, and two light rays that have been transmitted through those two openings 1304a and 1304b will produce multi-viewpoint images. In such a system, left and right viewpoint images are normally obtained by alternately opening and closing those openings 1304a and 1304b. According to this technique, however, by separating the two light rays transmitted through those two openings 1304a and 1304b from each other through image processing, the time lag that would otherwise be produced between the two images can be eliminated. For that purpose, a polarization filter that has a vertical polarization transmission axis is provided for the opening 1304a and a polarization filter that has a horizontal polarization transmission axis is provided for the opening 1304b. 
The image capturing section 1303 uses a polarization mosaic filter 1305 and an image sensor 1306 in combination. The polarization mosaic filter 1305 has a structure in which polarization filters 1305a with a vertical polarization transmission axis and polarization filters 1305b with a horizontal polarization transmission axis are alternately distributed spatially. The light rays that have been transmitted through the left and right openings 1304a and 1304b are transformed by this polarization film into two light rays, of which the polarization directions are perpendicular to each other. That is why the (polarized) light rays that have been transmitted through the openings 1304a and 1304b are incident on respective portions of the polarization mosaic filter 1305 that have their associated polarization transmission axes. In this manner, based on the signals of the pixels that are covered with the polarization filter 1305a and the signals of the pixels that are covered with the polarization filter 1305b, the intensities of the light rays that have been transmitted through the openings 1304a and 1304b can be detected. As a result, two different kinds of images can be obtained as multi-viewpoint images.